Abstract

We describe a new approach for on-chip optical non-reciprocity which makes use of strong optomechanical interaction in microring resonators. By optically pumping the ring resonator in one direction, the optomechanical coupling is only enhanced in that direction, and consequently, the system exhibits a non-reciprocal response. For different configurations, this system can function either as an optical isolator or a coherent non-reciprocal phase shifter. We show that the operation of such a device on the level of single-photon could be achieved with existing technology.

(a) Transmission |tR/L|2 of the OM system when operated as an optical isolator (κin = κ). Within the resonator bandwidth, the left-moving field is attenuated while the right-moving field is almost completely transmitted. For this plot GR = 5κ. (b) Non-reciprocal phase shifter (κin = 0.01κ). Both the left and the right input field are almost completely transmitted (> 98%), but acquire different phases, Δθ = θR − θL. Black lines show the location of resonances. For these plots γm = 0.

General add-drop configuration, which can be employed for non-reciprocal photon routing between the upper and lower waveguide. It reduces to the resonator coupled to a single waveguide, if the coupling to the lower waveguide is absent (κ′ = 0).

Mean photon number in the left and right circulating modes in the presence of a finite mode coupling β and as a function of the pump detuning Δ = ωL−ωc. For this plot we have assumed that the pump field only drives the right-circulating mode and that the resonator is coupled to a single waveguide (κ′ = 0). The other parameters are (β,κin)/κ = (4,1). At the normal mode frequencies ω ≃ ±β, the left- and right-circulating modes are almost equally populated, while everywhere else, there is an intensity imbalance between left- and right-circulating modes. (b) The diagram shows the relation between the relevant frequencies in the system. In the presence of the mode coupling, the sidebands (±β) are located around the bare resonator frequency ωc and the resonator is pumped at the mechanical red sideband.

Transmittance for light propagating in a waveguide coupled to a resonator (AFP), in the presence of (a) weak (β = 2κ) and (b) strong (β = 8κ) mode mixing. For these plots we have assumed (ωm, GR,κin,γm)/κ = (20,5,1,0) and Δ = −ωm.

Operational bandwidth of an optical diode in the presence of a finite mode coupling β and different values of the enhanced OM coupling GR. For this plot we have assumed GL = 0 and (ωm,κin,γm)/κ = (20,1,0), Δ = −ωm. In the absence of the mode coupling the bandwidth is 4κ, which for a finite β can be recovered by using a strong pump to enhance |GR|.